Pentachloro(pyrazine)rhenate(IV) Complex as Precursor of heterobimetallic pyrazine-containing ReIV2MII (M = Ni, Cu) Species : Synthesis, Crystal Structures and Magnetic Properties

Three novel Re(IV) mononuclear complexes of formulae NBu4[ReCl5(pyz)] (1), NH2Me2[ReCl5(pyz)] (2) and NH4[ReCl5(pyz)] center dot 0.75H(2)O (3), (pyz being pyrazine; NBu4+ = tetra-n-butylammonium cation, NH2Me2+ = dimethylammonium cation and NH4+ = ammonium cation), were synthesized by ligand substitution reaction from [ReCl6](2-) anion and pyrazine in N, N-dimethylformamide (DMF). In addition, two new heterobimetallic compounds, the salt namely [ReCl5(pyz)](2)[Ni(cyclam)] (4) (cyclam = 1,4,8,11-tetraazacyclotetradecane) and the heterotrinuclear [{ReCl5(mu-pyz)}(2)Cu(DMF)(4)] (5) complex, were prepared by using as precursor 1 and 3, respectively. Compounds 1-5 were characterized by single-crystal X-ray diffraction. 1-3 are made up of discrete [ReCl5(pyz)](-) anions and NBu4+ (1), NH2Me2+ (2) and NH4+ (3) cations. [ReCl5(pyz)](-) unit interacts toward Ni(II) (4) and Cu(II) (5) metal ions through different modes. In 4 two [ReCl5(pyz)](-) anions weakly interact with a [Ni(cyclam)](2+) cation through chloro atoms, while compound 5 is a heterotrinuclear pyrazine-bridged Re-IV Cu-2(II) complex made up of [ReCl5(pyz)](-) anions and [Cu(DMF) 4] 2+ cations. The magnetic properties of 1-5 were investigated in the temperature range 1.9-300 K. The magnetic behaviour of 1 is that of a magnetically diluted Re(IV) complex with a large value of zero-field splitting of the ground state (|2D| is ca. 18.8(1) cm(-1)), whereas those of 2 and 3 are typical of antiferromagnetically coupled systems exhibiting susceptibility maxima at 10 (2) and 12 K (3). Compound 4 shows antiferromagnetic interactions between Re(IV) metal ions, Ni(II) being diamagnetic (because of its square-planar geometry), while 5 exhibits a ferromagnetic coupling between Re(IV) and Cu(II) metal ions across the pyrazine bridges with a J(ReCu) value of +11.8(1) cm(-1).